U.S. officials are considering prohibiting Americans from investing in Alibaba Group Holding Ltd. and Tencent Holdings Ltd., a potential escalation of the outgoing Trump administration’s efforts to unwind U.S. investors’ holdings in major Chinese companies.

State and Defense Department officials in recent weeks have discussed expanding a blacklist of companies prohibited to U.S. investments over alleged ties to China’s military and security services, according to people familiar with the matter. The U.S. government announced its original blacklist in November with 31 companies.

Tencent and Alibaba are China’s two most valuable publicly listed companies, with a combined market capitalization of over $1.3 trillion and scores of American mutual funds and other investors holding their shares. Alibaba’s New York-listed American depositary receipts fell more than 5% on Wednesday, while Tencent ADRs tumbled by about 4% in the U.S. over-the-counter market.

The blacklist is one of several Trump administration efforts related to investing in Chinese firms. Also on Wednesday, the New York Stock Exchange said it would delist three major Chinese telecommunication carriers targeted by a Trump executive order, after earlier scrapping the plan following “new specific guidance” from the Treasury Department.

The investment decisions aren’t the only steps the Trump administration has taken.